2nd Petrus-OPERA Conference on Radioactive Waste Management and Geological Disposal
72
Long term evaluation on the groundwater chemistry due to cement
materials with numerical simulation
Diego Sampietro1(diego.sampietro@amphos21.com), Elena Abarca1, Marti Bayer1, Salvador Jordana1, Jorge Molinero1, Tatsuya Tanaka2, Shuji Hashimoto2, Teruki Iwatsuki3, Hironori Onoe3
1 Amphos 21 Consulting, Passeig Garcia i Faria, 49-51, 08019, Barcelona, Spain
2 Obayashi Corporation, Shinagawa Intercity Tober B 2-15-2, Konan, Minato-ku. Tokyo 108-8502, Japan. 3 Japan Atomic Energy Agency, 1-64, Yamanouchi, Akeyo-cho, Mizunami-shi, Gifu, 509-6132, Japan
Introduction
The Japan Atomic Energy Agency (JAEA) is being carried out the Mizunami Underground Research Laboratory project in Mizunami city, central Japan. This laboratory is a purpose-built generic URL (Underground Research Laboratory) that is planned for a scientific study of the deep geological environment as a basis of research and development for geological disposal of high-level radioactive wastes. As part of the project, groundwater flow model has been developed using the commercial software ConnectFlow, which is capable to generate hydrogeological models but it cannot account for chemical processes. It is important to evaluate the effect of the cement materials present in the underground facility in the groundwater. Development of modelling method for understanding the temporal evolution of the concrete structures is a key process in the radioactive waste storage.
The objective of this study was to develop a reactive transport model that reproduces the evolution of the hyperalkaline plume in the bedrock, which is supposed to be generated by the concrete degradation. The precipitation of secondary minerals can reduce porosity up to the point to induce important changes on hydraulic conductivity.
Methods
The reactive transport model have been developed using iCP (interface COMSOL-PHREEQC)[1]. COMSOL[2] is a commercial software that solves a large range of different process, such as flow or conservative transport, using the finite element method. PHREEQC [3] is a well-known program which can be used as a speciation program to calculate saturation indices, the distribution of aqueous species, and the density and specific conductance of a specified solution composition.
The model developed is formed by the URL located in the middle of a “box” formed by granitic materials. The geometry and the spatial distribution of hydrogeological conditions (hydraulic conductivity and porosity fields) have been implemented in COMSOL from the ConnectFlow files (Figure 1 and Figure 2). The URL consists of two 500 m deep shafts and several galleries. In addition to concrete lining (blue area in the Figure 1), grout has been injected to minimize groundwater inflow volume. Grouted area matches with the volume in contact with concrete lining in this model (Figure 1).
iCP uses COMSOL[2] to solve the flow and the transport. The chemical part is solved by PHREEQC. The groundwater flow model has been implemented using the Darcy’s law physics and the transport process is implemented using a custom physics interface named as Molal Solute Transport.
The chemical composition of the grout is half of the portlandite and half of the CSH (1.67). This is a simplified composition taking into account the principal components involved in the alkalinity. The chemical composition of the groundwater has been obtained from Iwatsuki et al.[4]. Basically, this groundwater is in equilibrium with granites and has a pH of about 8.5.
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2 Discussion Portlandite where the w meters of de Figure 3: G Groundwat The high pH but its exte downstream of pore velo as a result p The mixing main miner almost the n The hydrau present pre This study geochemist long-time si References [1] A.Nardi, efficient Geoscie [2] COMSO [3] D.L.Park Compute Geochem Geologic [4] T. Iwatsu research 2nd Petrus-OPE n degradation water pore v epth below t Groundwate ter flows so H plume caus ension is lim m. The high e ocities. In the produce less between th rals (CSH(0.8 natural initial ulic shadow cipitation of shows that try. iCP allow
mulations. s and Citatio A.Idiart, P.T numerical fra nces, doi:10 OL. COMSOL khurst and C er Program f mical Calcula cal Survey W uki, R. Furue h laboratory ( ERA Conferen is higher in velocity is h he sediment er pH and d outhwards. sed by disso mited and b extension of ese two area s dilution. e grout wate 83); hydrota values. area locate mineral phas iCP is a flex ws to incorpo ons Trinchero, L.M amework for .1016/ j.cage L Multiphysic C.A.Appelo. D for Speciatio ations. Chap Water-Resour e, H.Mie, S.Io (MIU)”. Appli nce on Radioa n the laborat igher. The h ary rocks. different mi olution of por uffered. Hig the pH value as, the mixin
er and the n lcite and ca d downstrea ses. The sam xible and po orate geoche M.de Vries a r the solution eo. 2014.04. s Reference Description o n, Batch-Rea pter 53 of Sec rces. 2013. oka and T.M ied Geochem active Waste M 74 tory zone lo highest portla ineral preci rtlandite and gh values of es > 11 are ng between t native groun lcite), occup am the labo me effect is a owerful tool emical proces nd J.Moliner n of coupled m 011. 2014. e Guide. Vers of Input and E action, One-ction A, Grou Mizuno,” Hydr mistry, 20, 22 Management a ocated upstre andite degra ipitation for CSH extend f pH (pH > located in tw the “grout wa dwater prod pying a large oratory, whic also observed for quantitat sses in 3D la ro, “”Interface multiphysics sion 5.2. Bur Examples fo Dimensional undwater boo rochemical b 283-2302. 20 and Geologica eam (northe adation rates r a simulati ds towards th 11) extend wo areas cha ater” and the uces precipi er extension h presents d for the sed tive integratio arge scale C e Comsol-PH and geoche ilington, MA: r PHREEQC Transport, a ok 6, Modelin baseline cond 005. al Disposal ern border) a s are located ion time of he downstrea d less than aracterized b e native wate itation of fol and bufferin pH higher t dimentary roc on of hydrog COMSOL mo HREEQC (iC emistry”, Com : COMSOL In C Version 3— and Inverse ing Techniqu dition of grou and in areas d about 200 500 years. am direction, 100 meters y low values er is smaller, lowing three ng the pH to than 11, not ck domain. geology and odels and for
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